Various single-channel and/or multi-channel audio rendering systems such as 5.1, 7.1 or 9.1 multi-channel audio rendering systems are currently in use. The audio rendering systems allow e.g. for the generation of a surround sound originating from 5+1, 7+1 or 9+1 speaker locations, respectively. For an efficient transmission or for an efficient storing of the corresponding single-channel or multi-channel audio signals, audio codec (encoder/decoder) systems such as Dolby Digital (DD) or Dolby Digital Plus (DD+) are being used.
There may be a significant installed base of audio rendering devices which are configured to decode audio signals which have been encoded using a particular audio codec system (e.g. Dolby Digital). The particular audio codec system may be e.g. referred to as a second audio codec. On the other hand, the evolution of audio codec systems may lead to an updated audio codec system (e.g. Dolby Digital Plus), which may be e.g. referred to as a first audio codec system. The updated audio codec system may provide additional features (e.g. an increased number of channels) and/or improved coding quality. As such, content providers may be inclined to provide their content in accordance to the updated audio codec system.
Nevertheless, the user having audio rendering device with a decoder of the second audio codec system should still be able to render the audio content which has been encoded in accordance to the first audio codec system. This may be achieved by a so called transcoder or converter which is configured to convert the audio content which is encoded in accordance to the first audio codec system into modified audio content which is encoded in accordance to the second audio codec system.
A further need for transcoding may arise along the distribution chain of audio content. Audio content may be encoded by a content provider using an audio codec which is well suited for the production and the broadcasting of audio content (such as the Dolby E audio codec). The audio content may be distributed using this production-oriented audio codec, and the audio content may be transcoded in accordance to a second audio codec (such as the lossless codec Dolby TrueHD or such as the Dolby Digital Plus or the Dolby Digital codec).
The audio content is typically associated with metadata which is encoded in the bitstream representing the audio content. Usually, the audio content is split up in a sequence of frames, where each frame of audio content comprises a pre-determined number of samples (e.g. 1024 samples). A frame of the sequence of frames may be associated with a respective container or frame of metadata. The container of metadata may be indicative of information describing the frame of audio content that the container is associated with. An example for such information describing the frame may be loudness data regarding some or all of the samples of the frame. Alternatively or in addition, the container of metadata may be used to transmit auxiliary data which may not be directly associated with the corresponding frame of audio content. Such auxiliary data may e.g. be used to provide a decoder of an audio codec system with a firmware upgrade.
In addition to transcoding the audio content from a first audio codec system to a second audio codec system, the transcoder typically also needs to transcode the associated metadata. In order to reduce the cost of transcoders/converters (which are implemented e.g. within settop boxes), the computational complexity of the conversion between a first audio codec system and a second audio codec system should be relatively low. This should also be the case for the transcoding of the metadata. In the present document, methods and systems for transcoding are described, which allow for the transcoding of metadata with a reduced computational complexity.